Interest in the medicinal chemistry of quinazoline derivatives was stimulated in the early 1950's with the elucidation of the structure of a quinazoline alkaloid, 3-[β-keto-gamma-(3-hydroxy-2-piperidyl)-propyl]-4-quinazolone, from an Asian plant known for its antimalarial properties. In a quest to find additional antimalarial agents, various substituted quinazolines have been synthesized. Of particular import was the synthesis of the derivative 2-methyl-3-o-tolyl-4-(3H)-quinazolinone. This compound, known by the name methaqualone, though ineffective against protozoa, was found to be a potent hypnotic.
Since the introduction of methaqualone and its discovery as a hypnotic, the pharmacological activity of quinazolinones and related compounds has been investigated. Quinazolinones and derivatives thereof are now known to have a wide variety of biological properties including hypnotic, sedative, analgesic, anticonvulsant, antitussive and anti-inflammatory activities.
Quinazolinone derivatives for which specific biological uses have been described include U.S. Pat. No. 5,147,875 describing 2-(substituted phenyl)-4-oxo quinazolines with bronchodilator activity. U.S. Pat. Nos. 3,723,432, 3,740,442, and 3,925,548 describe a class of 1-substituted-4-aryl-2(1H)-quinazolinone derivatives useful as anti-inflammatory agents. European patent publication EP 0 056 637 B1 claims a class of 4(3H)-quinazolinone derivatives for the treatment of hypertension. European patent publication EP 0 884 319 A1 describes pharmaceutical compositions of quinazolin-4-one derivatives used to treat neurodegenerative, psychotropic, and drug and alcohol induced central and peripheral nervous system disorders.
Quinazolinones are among a growing number of therapeutic agents used to treat cell proliferative disorders, including cancer. For example, PCT WO 96/06616 describes a pharmaceutical composition containing a quinazolinone derivative to inhibit vascular smooth cell proliferation. PCT WO 96/19224 uses this same quinazolinone derivative to inhibit mesengial cell proliferation. U.S. Pat. Nos. 4,981,856, 5,081,124 and 5,280,027 describe the use of quinazolinone derivatives to inhibit thymidylate synthase, the enzyme that catalyzes the methylation of deoxyuridine monophosphate to produce thymidine monophosphate which is required for DNA synthesis. U.S. Pat. Nos. 5,747,498 and 5,773,476 describe quinazolinone derivatives used to treat cancers characterized by over-activity or inappropriate activity of tyrosine receptor kinases. U.S. Pat. No. 5,037,829 claims (1H-azol-1-ylmethyl) substituted quinazoline compositions to treat carcinomas which occur in epithelial cells. PCT WO 98/34613 describes a composition containing a quinazolinone derivative useful for attenuating neovascularization and for treating malignancies. U.S. Pat. No. 5,187,167 describes pharmaceutical compositions comprising quinazolin-4-one derivatives which possess anti-tumor activity.
Other therapeutic agents used to treat cancer include the taxanes and vinca alkaloids. Taxanes and vinca alkaloids act on microtubules, which are present in a variety of cellular structures. Microtubules are the primary structural element of the mitotic spindle. The mitotic spindle is responsible for distribution of replicate copies of the genome to each of the two daughter cells that result from cell division. It is presumed that disruption of the mitotic spindle by these drugs results in inhibition of cancer cell division, and induction of cancer cell death. However, microtubules form other types of cellular structures, including tracks for intracellular transport in nerve processes. Because these agents do not specifically target mitotic spindles, they have side effects that limit their usefulness.
Improvements in the specificity of agents used to treat cancer is of considerable interest because of the therapeutic benefits which would be realized if the side effects associated with the administration of these agents could be reduced. Traditionally, dramatic improvements in the treatment of cancer are associated with identification of therapeutic agents acting through novel mechanisms. Examples of this include not only the taxanes, but also the camptothecin class of topoisomerase I inhibitors. From both of these perspectives, mitotic kinesins are attractive targets for new anti-cancer agents.
Mitotic kinesins are enzymes essential for assembly and function of the mitotic spindle, but are not generally part of other microtubule structures, such as in nerve processes. Mitotic kinesins play essential roles during all phases of mitosis. These enzymes are “molecular motors” that transform energy released by hydrolysis of ATP into mechanical force which drives the directional movement of cellular cargoes along microtubules. The catalytic domain sufficient for this task is a compact structure of approximately 340 amino acids. During mitosis, kinesins organize microtubules into the bipolar structure that is the mitotic spindle. Kinesins mediate movement of chromosomes along spindle microtubules, as well as structural changes in the mitotic spindle associated with specific phases of mitosis. Experimental perturbation of mitotic kinesin function causes malformation or dysfunction of the mitotic spindle, frequently resulting in cell cycle arrest and cell death.
Among the mitotic kinesins that have been identified is KSP. KSP belongs to an evolutionarily conserved kinesin subfamily of plus end-directed microtubule motors that assemble into bipolar homotetramers consisting of antiparallel homodimers. During mitosis KSP associates with microtubules of the mitotic spindle. Microinjection of antibodies directed against KSP into human cells prevents spindle pole separation during prometaphase, giving rise to monopolar spindles and causing mitotic arrest and induction of programmed cell death. KSP and related kinesins in other, non-human, organisms, bundle antiparallel microtubules and slide them relative to one another, thus forcing the two spindle poles apart. KSP may also mediate in anaphase B spindle elongation and focussing of microtubules at the spindle pole.
Human KSP (also termed HsEg5) has been described [Blangy, et al., Cell, 83:1159-69 (1995); Whitehead, et al., Arthritis Rheum., 39:1635-42 (1996); Galgio et al., J. Cell Biol., 135:339-414 (1996); Blangy, et al., J. Biol. Chem., 272:19418-24 (1997); Blangy, et al., Cell Motil Cytoskeleton, 40:174-82 (1998); Whitehead and Rattner, J. Cell Sci., 111:2551-61 (1998); Kaiser, et al., JBC 274:18925-31 (1999); GenBank accession numbers: X85137, NM004523 and U37426], and a fragment of the KSP gene (TRIPS) has been described [Lee, et al., Mol. Endocrinol., 9:243-54 (1995); GenBank accession number L40372]. Xenopus KSP homologs (Eg5), as well as Drosophila KLP61 F/KRP1 30 have been reported.
Mitotic kinesins are attractive targets for the discovery and development of novel mitotic chemotherapeutics. Accordingly, it is an object of the present invention to provide methods and compositions useful in the inhibition of KSP, a mitotic kinesin.